1. Technical Field
The present invention relates to a method of surface treatment of semiconductor. More particularly, the present invention relates to a dry etching method of removing native oxide film formed on the silicon exposed in a contact hole of a semiconductor device to be used for burying an electrode material such as polysilicon, doped polysilicon, metal, TiSi2, WSi2 or TiN and/or scum produced as a result of the reaction of resist and silicon in a process of manufacturing a semiconductor device on a silicon wafer.
2. Background Art
The native oxide film formed in a contact hole is used to be removed by chemical dry etching or IPA (isopropyl alcohol) cleaning in early days. However, such a method is no longer adaptable to the current situation where contact holes are remarkably downsized and large aspect ratios are adopted.
Japanese Patent Application Laid-Open Publication No. 5-275392 discloses a single wafer native oxide film removing device to be used for semiconductor silicon wafers (to be referred to simply as “wafer” hereinafter). According to the above identified patent document, the native oxide film is etched off by causing a plasma-excited mixture gas of NF3 and H2 to flow into a downstream reactor, while cooling the wafer to about 173 K (−100° C.) by way of a susceptor. The etching process can be suspended when (NH4)2SiF6 or a similar substance is formed on the wafer. Then, the wafer is irradiated with inactivated Ar plasma in order to make the etching process start again.
A method of etching off SiO2 (native oxide film) by using NF3 and NH3 has also been disclosed (1999 DRY PROCESS SYMPOSSIUM, In-situ observation of Si Native Oxide Removal Employing Hot NH3/NF3 Exposure, Ogawa et al. pp. 273-278). According to the above identified paper, the native oxide film formed on a wafer is removed by dissociating (NH4)2SiF6 at temperature exceeding 100° C. The paper also says that the reaction product may probably be NH4F. HF or NH4F. In the following description, the reaction product of the source gas is referred to as etching gas.
With the known single wafer native oxide film removing method, the reaction time including a cooling operation, a plasma etching operation and an operation of removing the reaction product is about four minutes per wafer. Then, the total time required for the reaction including the overhead time of introducing and drawing out the wafer is about seven minutes. Thus, the overall process of removing the native oxide film inevitably includes the overhead time of letting each wafer in and out to consequently give rise to a bottle neck for the manufacturing line. While this sort of problem may be avoided when a vertical batch method such as a low pressure CVD (LPCVD) method is used for removing the native oxide film, no such method has been proposed to date. Additionally, with the conventional single wafer native oxide film removing method, it is indispensable to cool the wafer to below 293 K by way of a susceptor in order to reduce the time required for the treatment by raising the etching rate. Such a cooling technique by turn involves the use of a complicated cooling system.